The present invention relates generally to the field of electronic data storage and retrieval, and more particularly to a perpendicular magnetic recording head having a coil formed on a planar surface and wrapped around the top writing pole.
A magnetic recording head generally consists of two portions, a writer portion for storing magnetically-encoded information on a magnetic disc and a reader portion for retrieving that magnetically-encoded information from the disc. The reader portion typically consists of a bottom shield, a top shield, and a sensor, often composed of a magnetoresistive (MR) material, positioned between the bottom and top shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover the data that was encoded on the disc.
The writer portion of the magnetic recording head typically consists of a top pole and a bottom pole, which are separated from each other at an air bearing surface of the writer by a gap layer, and which are connected to each other at a region distal from the air bearing surface by a back via. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers, which typically form a hill which is thinner near the air bearing surface than it is toward the center of the writer. The shape of the top pole, which is formed on this hill, typically follows the contour of the hill. The air bearing surface is the surface of the recording head immediately adjacent the magnetic medium or disc. The writer portion and the reader portion are often arranged in a merged configuration in which a shared pole serves as both the top shield of the reader portion and the bottom pole of the writer portion.
To write data to the magnetic medium, an electrical current is caused to flow through the conductive coils, thereby inducing a magnetic field across the write gap between the top and bottom poles. By reversing the polarity of the current through the coils, the polarity of the data written to the magnetic media is also reversed. Because the top pole is generally the trailing pole of the top and bottom poles, the top pole is used to physically write the data to the magnetic media. Accordingly, it is the top pole that defines the track width of the written data. More specifically, the track width is defined by the width of the top pole at the air bearing surface.
A common configuration for the conductive coils within the writer is a “pancake” coil configuration in which the coils wrap around the back via in a plane substantially normal to the air bearing surface. Because the pancake coils extend relatively far into the writer and away from the air bearing surface, the pancake coils are necessarily long. Additionally, the pancake coils are highly inefficient since the pancake coils wrap around only a small portion of the top pole (that is, only the back via), resulting in inefficient generation of magnetic flux in the pole for a given current through the coils. Accordingly, it is necessary to have greater number of coil turns around the back via to overcome this inefficiency of the pancake coils. Third, the frequency response of the writer is low due to the large number of coil turns required and the overall length thereof, as the greater length of the coils requires a greater amount of time to reverse the direction of current through the coils.
One solution to the pancake coil configuration of the conductive coils is the vertical (or solenoidal) coil configuration in which the coils are wrapped vertically around the top pole. In this configuration, a lower layer of coils is provided between the top and the bottom poles and an upper layer of coils is provided above the top pole. The upper and lower layers of coils are then connected to each other using conventional methods to form a single vertical coil.
The vertical coil configuration offers improved efficiency over the pancake coil configuration, in that a greater percentage of the top pole is wrapped by the coils, and thus requires fewer number of coil turns around the top pole. Additionally, the configuration allows for a shorter length of coil per coil turn. The shorter overall length of the vertical coil configuration thus offers improved frequency response over the pancake coil configuration.
Nonetheless, both of these prior art configurations have a distinct limitation. In both configurations, the top pole is formed over a mound of coils resulting in the top pole having a “bump” shape. As described above, the track width of the written data is defined by the width of the top pole at the air bearing surface. In both of these configurations, however, the portion of the top pole adjacent the air bearing surface is sloped. It is therefore difficult to precisely control the width of the top pole at the air bearing surface, particularly as the width necessarily becomes smaller to allow for greater data storage densities. This is particularly important in perpendicular recording devices designed to operate with extremely high data storage densities and small track widths. Perpendicular recording is similar to conventional longitudinal recording, except that data is recorded by magnetic flux flowing from the writer pole, through a recording layer of the magnetic medium, into a soft underlayer of the medium, and then back through a flux return pole of the writer. Accordingly, there is a need for a perpendicular recording write head with a planar top pole design that can efficiently function at high bit densities.